We have witnessed weeks of setbacks and speculation that the 13-year-old experiment of economic and monetary union (EMU) may be about to break up. Now France and Germany have drawn together to try to forge what the German chancellor, Angela Merkel, calls "a new phase of European integration" in a form of fiscal union. However, there are still a great many hurdles before we will reach a solution.

Abetting Merkel and President Nicolas Sarkozy of France is Mario Monti, former European commissioner, now heading a technocratic government in Rome. Germany, France and Italy are by far the largest economies in the 17-nation euro area.

The trio have thus refashioned the "gang of three" concept that launched EMU at a 12-country summit in Maastricht in the Netherlands exactly 20 years ago, on 9 December 1991, with a compact between President François Mitterrand of France, the German chancellor, Helmut Kohl, and Giulio Andreotti, the Italian premier.

Monti, a welcome substitute for Silvio Berlusconi, has presided over a steep decline in Italian 10-year bond borrowing costs in recent days. This is a sign that decisions on budget austerity in Rome are starting to find positive resonance on financial markets. At an economic conference in Warsaw in October, when he was given a rapt reception as de facto prime minister-in-waiting, Monti reflected that EMU's future lay in "more market, more discipline, more Europe and more Germany". All four characteristics will be on display at Friday's Brussels meeting.

However, the experience of a dozen or so European crisis gatherings in the past 18 months shows that much more is needed than summit declarations. Jürgen Stark, the European Central Bank board member who will step down at the end of this month partly because he disagrees with ECB purchases of the bonds of weaker EMU members, has summed up the problem: "The half-life value of European decision-making is astonishingly short."

Tampering with the complicated EMU edifice resembles an attempt to repair a complex, many-sided piece of machinery where every component influences in a different way every other element in the mechanism. Apparently benign, constructive action to improve the workings of one small cog in the machine produces a negative outcome elsewhere. John Major, Britain's prime minister at Maastricht, referred then to juggling with different countries' sensitivities as "12-dimensional chess". Since then, with 27 countries in the European Union, the convolutions are still greater.

To take one example, Merkel made a major concession to France and the ECB on Monday in Paris when she said private sector bond-holders would no longer need to take losses on future euro area rescue packages. However, either the public sector would have to pick up a greater share of the bill – anathema to Merkel and her Berlin coalition; or the trouble-torn states at the centre of the debt crisis would have to make still further efforts to pay back their loans in full. This would intensify the vicious circle of debt deflation in the peripheral countries, producing more austerity, more income losses, less tax revenue and ultimately fewer funds to repay debts.

Another case relates to the credit rating of the euro area's triple A-rated countries, including Germany, France, Austria, Finland, the Netherlands and Luxembourg. Massive financing for peripheral states deprived of normal access to bond markets will be required in years ahead. The announcement on Monday night by Standard & Poor's that it may downgrade the triple A states underlines how the creditors may suffer if bailout terms for the debtors are too generous – stiffening Merkel's resolve to be as tough as possible on errant euro members.

Perhaps the most serious issue concerns renegotiating the European treaties towards closer fiscal union. France is insisting that changes be incorporated in an inter-governmental framework that would be prone to political horse-trading and insufficient to convince either the Germans or the ECB that governments are really living up to their responsibilities. Shifting treaty language towards much greater centralised control of budgets would be highly difficult to pass through referendums in key countries, particularly Ireland. Agreeing a treaty for all 27 EU members with sufficient centralisation to please the Germans, but with enough flexibility to win British support, would be a near-impossible task.

On the other hand, limiting a new treaty only to the 17 EMU members would bring confrontation with Poland and Sweden, two intensely pro-European countries that wish eventually to join EMU but will almost certainly stay outside for the next five years. So even if Europe's battling governmental teams pass the milestone of Friday's crisis get-together, they will need many more positive results on and off the summitry field before a genuine solution becomes visible.